Long speech made by saint on faith (6)
I believe the answer is:
screed
'long speech' is the definition.
(I've seen this before)
'saint on faith' is the wordplay.
'saint' becomes 's'.
'on' means one lot of letters go next to another.
'faith' becomes 'creed' (I've seen this before).
's'+'creed'='SCREED'
'made by' acts as a link.
(Other definitions for screed that I've seen before include "Tediously long speech" , "lengthy document" , "Tiresomely long letter about creeds" , "A long written effusion" , "Mortar used for levelling" .)